If ours is the age of fragmentation in music, the novel, and art, then in architecture its theoretician was the Italian Bruno Zevi, who has died aged 81 of a coughing fit brought on by influenza. Initially a socialist, later a libertarian, he was fundamentally a Zionist. Deeply affected by his experience in the Mussolini era, he believed that all notions of architectural order, organisation, and clarity - as expressed in the bombastic buildings of Marcello Piacentini, an "official architect" of the time - were a cultural disease to be countered by an aesthetic of disorder, disruption and disturbance.

To this view he allied a vast learning and art-historical discipline absorbed from his contemporaries, the art historians and critics Ragghianti, Longhi and Briganti. He became Italy's most celebrated polemicist for architecture as a means of exposing what he saw as the evil ideas of classicism.

In 1940, forced by Mussolini's racial purity laws to leave Italy, Zevi studied at Harvard with Walter Gropius. Discovering an enthusiasm for Frank Lloyd Wright's conception of a democratic, open architecture, he returned to Italy in 1945, published Verso l'architettura organica (Towards Organic Architecture) and was offered the history chair at Venice school of architecture. In 1948, he published Saper Vedere la Città (How To Understand The City), which examined the influence on the city of Ferrara of the Renaissance architect Biagio Rossetti, and the interaction between architecture, urban fabric, economics, history and politics.

These two books alone place Zevi among the greatest historians and theoreticians. They were followed in 1948 by Saper vedere l'architettura (How To Look At Architecture) - still a favourite among Italian students - and Storia dell'Architettura Moderna (1950), a polemic against rationalist-centred history.

Moving to Rome university in 1963, Zevi created a school of first-class architectural historians. In 1970 he published Erich Mendelsohn: Complete Works, and in 1974 the brilliant Poetica dell'Architettura Neoplastica, which comprehensively explained the Dutch De Stijl movement of the 1920s and early 1930s. In 1979, with post-modernism in full flood, Zevi resigned his professorship in disgust.

Looking back at a particular kind of fascist architecture, Zevi convinced himself that columns, colonnades and symmetry were everywhere the language of repression and cruelty. Whether considering ancient Rome or the Renaissance, he saw architectural history as a battle between these styles of oppression and the anti-styles of liberation. He dedicated himself to rooting out neoclassicism, order, and symmetry wherever he found them - never questioning the validity of his own assumptions.

The intensity with which he often expressed himself might shock an English-speaking reader; when Ignazio Gardella died, Zevi sent that noble architect to his grave with cries of "obscene massacre" over a neo-classical project he had worked on with Aldo Rossi, a satan of the drawing-board whose architecture was filled with neoclassical references.

Zevi attacked everything: the American Louis Kahn's architecture "evoked the ambiguity of the taste of the emperor", while the Pantheon, a symmetrical dome (and therefore fascist) was liquidated as "claustrophobic". The other architectural interventions of Hadrian in Rome were only acceptable insofar as they could be read as "a break, a revolution in the continuum of the urban fabric, interrupting it, modifying it, deviating it".

In 1973, Zevi set out these ideas as a set of invariants - a sort of anti-classical codebook that attempted to define modernity as a language of asymmetry and dissonance, which he propagated via his magazine L'architettura, cronache e storia. This exciting theory of architecture as rupture and fragmentation marks him out as the seminal theoretician for all currents of modernism interested in iconoclasm and deconstruction, from Alvar Aalto in the 1930s to Daniel Libeskind in the 1990s.

Zevi also brought his provocative point of view to reviewing architectural events for the weekly L'Espresso, providing a link between the reader and the hermetic world of the architect. He passed judgment on everything, sometimes foolishly - writing off Bernini's St Peter's Square as a dreadful mess - sometimes presciently; he wrote in 1973 that James Stirling had "the gifts and the qualifications to become, if he wants to, the most important European architect".

Zevi was a major architectural scholar and polemicist; with his passing suddenly everything has gone flaccid; it is a disaster.

He married Tullia Calabi in 1940, although they later separated. He leaves a son and a daughter.

 Bruno Zevi, architectural historian and academic, born January 22 1918; died January 9 2000